The present invention relates to an apparatus and a method for drying a substrate and more particularly, to an apparatus and a method for drying a disk for a data storage device (hard drive) by controlled delivery of a polar organic compound, such as isopropyl alcohol (IPA), acetone, or methanol, and a hydrophobic organic compound, such as hydrofluoroether.
In the manufacture of LCD (liquid crystal display) panels, and hard drives, it is necessary to clean and dry the substrates for the above products, such as glass substrates, and disks, during the manufacturing process. The purpose of drying the substrates is to remove water on the substrates after cleaning. Currently several drying methods are being used in the electronic component industry. The methods include the spin-rinse dry method, the hot water slow pull method, the Marangoni-type process, the hot IPA process, and the hydrofluoroether process.
The spin-rinse dry uses centrifugal forces to remove water from substrate surfaces. However, spin-rinse dry is known to have problems such as water spotting, static electric charge build-up, and stress-induced substrate damage.
In the hot water slow pull method, the substrates are immersed in a hot water bath, which is heated to 80-90xc2x0 C., and then slowly pulled from the bath. When a substrate is pulled from the bath, a thin water film is formed on the surface of the substrate. Then, the thermal energy stored in the substrate evaporates the thin water film. For successful evaporation, the rate at which the substrate is separated from the bath must be matched to the evaporation rate. The hot water process has several shortcomings. When the substrate has a non-homogeneous surface, partly hydrophobic and partly hydrophilic, the substrate is likely to have stains thereon. Further, condensation of water vapor on the substrate after the substrate is pulled from the hot water may produce stains on the substrate.
The hot IPA process uses a large quantity of IPA, which is flammable, to fill the drying chamber. Accordingly, the hot IPA process is costly and environmentally unsafe.
The Marangoni-type process involves the introduction of a polar organic compound which dissolves in the liquid and thereby reduces the surface tension of the liquid. U.S. Pat. No. 6,027,574, entitled xe2x80x9cMETHOD OF DRYING A SUBSTRATE BY LOWERING A FLUID SURFACE LEVELxe2x80x9d, shows a Marangoni-type process. According to the Maringoni principle, fluid flows from low surface tension region to high surface tension region. In the Marangoni-type process, while the substrate is separated from the bath containing water that is at room temperature, the water is driven away from the substrate because of the Marangoni effect. To avoid condensation of water vapor on the surface of the substrate, the Marangoni-type process does not use hot water.
There are several issues with the conventional Marangoni-type process. First, the drying speed of the process is low, because the substrate is dried at room temperature, and the chamber is purged of IPA vapor remaining in the chamber after drying process for an extended period of time (3-5 minutes). Accordingly, the drying cost is high. Second, although room temperature water is used, there is still a condensation problem during and after the separation of the substrate from the water. Water vapor may condense on the substrate and form micro droplets that leave a residue behind, causing defects in subsequent manufacturing processes. Fourth, purging of IPA while the substrate is dried in the chamber may cause condensation of water vapor. Finally, although the conventional Marangoni-type process is safer than the hot IPA process, the quantity of IPA used in the conventional Marangoni-type process is still large enough to make the process environmentally unsafe.
The hydrofluoroether process uses hydrofluoroether as a drying agent. U.S. Pat. No. 6,119,366, entitled xe2x80x9cCHEMICAL DRYING AND CLEANING METHODxe2x80x9d, shows a hydrofluoroether process. Since this process uses only hydrofluoroether to directly displace water, the quantity of hydrofluoroether used in the drying process must be large, and thus the used hydrofluoroether needs to be recycled for reducing cost.
Accordingly, an effective drying process should be cost-effective, and should be environmentally safe, and should prevent the condensation of water on the substrate.
An aspect of the present invention provides a substrate dryer. A dryer in accordance with an embodiment of the present invention includes: a bath containing a fluid; a chamber; and a delivery system for supplying a polar organic compound, such as isopropyl alcohol, acetone, or methanol, and a hydrophobic organic compound, such as hydrofluoroether, perfluorocarbon, or hydrofluocarbon. The delivery system supplies isopropyl alcohol vapor and hydrofluoroether vapor to an interface between the substrate and the fluid while the substrate is being removed from the fluid of the bath into the chamber. The interface is the boundary between a portion of the substrate out of the fluid and a portion of the substrate in the fluid. The isopropyl alcohol vapor and hydrofluoroether vapor may be combined with a carrier gas, such as nitrogen.
The dryer further includes a chamber environment control system that supplies a heated gas into the chamber to dry the substrate and exhaust remaining hydrofluoroether vapor, remaining isopropyl alcohol vapor, and water vapor. The chamber environment control system includes: a gas inlet through which the gas is supplied into the chamber; a gas outlet through which the gas is removed from the chamber; and a gas heater that heats the gas before the gas is supplied into the chamber. The chamber environment control system controls the temperature and humidity in the chamber. The gas inlet is at a top portion of the chamber, and the gas outlet is at the bottom portion of the chamber. Further, a variable speed fan is connected to the gas outlet to draw the gas from the chamber.
The dryer further includes a fluid circulation system that circulates the fluid in the bath and a substrate transfer system that transfers the substrate into and out of the fluid of the bath. The fluid circulation system includes: a pump for circulating the fluid into and out of the bath; and a filter through which the fluid from the bath passes before being supplied into the bath. The substrate transfer system includes: a nest containing the substrate therein; and an arm that moves so that the substrate in the nest is immersed into and removed from the fluid of the bath.
The dryer further includes: a chamber heater attached to the chamber to transfer thermal energy into the chamber and an overflow tank for receiving overflow of the fluid from the bath; a fluid heater to heat the fluid in the bath; and a condenser unit. The condenser unit condenses exhausted hydrofluoroether vapor, isopropyl alcohol vapor, and water vapor to liquid for proper disposal.
Another aspect of the present invention provides a method of drying a substrate. A drying method in accordance with the present invention includes: immersing a substrate into a fluid contained in a bath; removing the substrate from the fluid into a chamber; and supplying a polar organic compound, such as isopropyl alcohol vapor, and a hydophobic organic compound, such as hydrofluoroether, to an interface between the substrate and the fluid.
Introduction of the isopropyl alcohol vapor forms a thin layer of a mixture of isopropyl alcohol vapor and fluid at the interface, increasing the wettability of substrate and promoting removal of the fluid when the substrate is removed from the fluid. Hydrofluoroether assists repelling of the fluid and forms a thin hydrofluoroether film on the surface of the substrate to prevent condensation of water vapor on the substrate.
The method further includes: supplying a gas into the chamber to dry the substrate; heating the gas before supplying the gas into the chamber; and removing the gas. While the gas is removed, the water vapor and the remaining isopropyl alcohol and hydrofluoroether vapor are also removed.
The method further includes: circulating the fluid into and out of the bath; heating the fluid; and filtering the fluid before the fluid is supplied into the bath. The method further includes heating the chamber to transfer thermal energy into the chamber.